proc: uid_cputime: create uids from kuids

Create uids from kuids using from_kuid_munged(),
otherwise we run into following build error and warnings:
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  CC      drivers/misc/uid_cputime.o
drivers/misc/uid_cputime.c: In function ‘uid_stat_show’:
drivers/misc/uid_cputime.c:90:36: error: incompatible type for argument 1 of ‘find_or_register_uid’
drivers/misc/uid_cputime.c:54:26: note: expected ‘uid_t’ but argument is of type ‘kuid_t’
drivers/misc/uid_cputime.c:94:4: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘kuid_t’ [-Wformat]
drivers/misc/uid_cputime.c: In function ‘process_notifier’:
drivers/misc/uid_cputime.c:194:6: error: incompatible types when assigning to type ‘uid_t’ from type ‘kuid_t’
make[2]: *** [drivers/misc/uid_cputime.o] Error 1
--------------------

Change-Id: Ifecb98001f7fe2fac74d1ef3e1abd03d43fc9059
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
(cherry picked from commit b0f4decae627cf2d74e6f72c7ecb939c77d48625)