drivers: qcom: rpmh: fix unwanted error check for get_tcs_of_type()

The patch fixes the bug reported by Dan Carpenter.
It removes the unnecessary err check for ‘tcs’ reported by
static checker warning:

drivers/soc/qcom/rpmh-rsc.c:111 tcs_invalidate()
warn: 'tcs' isn't an ERR_PTR
See also:
drivers/soc/qcom/rpmh-rsc.c:178 get_tcs_for_msg() warn: 'tcs' isn't
an ERR_PTR
drivers/soc/qcom/rpmh-rsc.c:180 get_tcs_for_msg() warn: 'tcs' isn't
an ERR_PTR

https://www.spinics.net/lists/linux-soc/msg04624.html

Fixes: 9a3afcfb

 ("drivers: qcom: rpmh-rsc: allow invalidation
of sleep/wake TCS")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Raju P.L.S.S.S.N <rplsssn@codeaurora.org>
Reviewed-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>