char: mspec: Use kvzalloc() in mspec_mmap()

Use kvzalloc() in mspec_mmap() instead of open-coding it.

Signed-off-by: Denis Efremov <efremov@linux.com>
Link: https://lore.kernel.org/r/20200827213421.50429-1-efremov@linux.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>