video: tegra: host: Use unsigned integer in sysfs

Sync point values are unsigned, but sysfs creates the text
representation as signed. Correct to use unsigned representation.

Bug 1039058

Change-Id: I96de13952eeeba9510bae179a036459ddee18dcd
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/128075
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Juha Tukkinen <jtukkinen@nvidia.com>
Reviewed-by: Michal Pecio <mpecio@nvidia.com>