msm: sps: Add integer wrap check for debugfs buffer

When converting debugfs buffer size to kilobytes value
there is a possible integer overflow and it may result
into negative value.

Fix the issue by adding integer wrap check for buffer
size just before conversion.

CRs-fixed: 564177
Change-Id: If4615561ea6a1c58e8be8c1b72f7881c068d8520
Signed-off-by: Dipen Parmar <dipenp@codeaurora.org>