drivers: shs: Alter file read and writes

Make cat and echo shell commands aimed to query SHS
shared memory files simply return 0.

Also equip recovery related global variables with
refcounts to prevent premature freeing when both
shs and shell commands may be opening and closing
the files.

[ 4993.922290]BUG: sleeping function called from invalid context at include/linux/uaccess.h:131
[ 4993.922306]Preemption disabled at:
[ 4993.922318][<ffffffaf240cfad8>] rmnet_shs_wq_ep_lock_bh+0x18/0x20 [rmnet_shs]
[ 4993.922333]Call trace:
[ 4993.922355] ___might_sleep+0x208/0x218
[ 4993.922357] __might_sleep+0x50/0x88
[ 4993.922363] __might_fault+0x44/0x98
[ 4993.922367] rmnet_shs_read+0x58/0xc8 [rmnet_shs]

Change-Id: I6ac5728e76980d5b74b9b415bd50a1a8147c266b
Signed-off-by: Conner Huff <chuff@codeaurora.org>