Fix spelling

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Haakan T Johansson <f96hajo@chalmers.se>
Closes #5547 
Closes #5543

config/kernel-mkdir-umode-t.m4

@@ -4,7 +4,7 @@ dnl # The VFS .create, .mkdir and .mknod callbacks were updated to take a
 dnl # umode_t type rather than an int.  The expectation is that any backport
 dnl # would also change all three prototypes.  However, if it turns out that
 dnl # some distribution doesn't backport the whole thing this could be
-dnl # broken apart in to three seperate checks.
+dnl # broken apart in to three separate checks.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_MKDIR_UMODE_T], [
 	AC_MSG_CHECKING([whether iops->create()/mkdir()/mknod() take umode_t])

config/kernel-xattr-handler.m4

@@ -296,7 +296,7 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_XATTR_HANDLER_LIST], [
 	dnl # 4.5 API change,
 	dnl # The xattr_handler->list() callback was changed to take only a
-	dnl # dentry and it only needs to return if it's accessable.
+	dnl # dentry and it only needs to return if it's accessible.
 	AC_MSG_CHECKING([whether xattr_handler->list() wants simple])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/xattr.h>

config/user-commands.m4

@@ -95,7 +95,7 @@ AC_DEFUN([ZFS_AC_CONFIG_USER_COMMANDS_COMMON], [
 ])
 
 dnl #
-dnl # Linux commands, used withing 'is_linux' blocks of test scripts.
+dnl # Linux commands, used within 'is_linux' blocks of test scripts.
 dnl # These commands may take different command line arguments.
 dnl #
 AC_DEFUN([ZFS_AC_CONFIG_USER_COMMANDS_LINUX], [