qseecom: Fix unprotected userspace access

After enabling KASan, unprotected userspace access causes
a PTE translation fault as it can cover only kernel memory
region. To fix this, we should use the correct API to access
user space memory region.

Change-Id: I1eba7d738d00e40b411c2a63dcf41417cfd7dd0f
Signed-off-by: Se Wang (Patrick) Oh <sewango@codeaurora.org>