fs/exec.c: replace opencoded set_mask_bits()

fs/exec.c: replace opencoded set_mask_bits()

Link: http://lkml.kernel.org/r/1548275584-18096-2-git-send-email-vgupta@synopsys.com
Link: http://lkml.kernel.org/g/20150807115710.GA16897@redhat.com
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Reviewed-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>