Allow shell to read/search /dev/input directory.

Resolves denials such as:
avc: denied { read } for pid=16758 comm="getevent" name="input" dev="tmpfs" ino=6018 scontext=u:r:shell:s0 tcontext=u:object_r:input_device:s0 tclass=dir

Change-Id: I709bd20a03a5271382b191393d55a34b0b8e4e0c
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>