This patch fixes a bug in function ConvertToGLint. This function
should convert ParamType into GLint instead of GLenum.

This patch can fix the bug that no errors are generated when trying
to set negative base level or max level by glTexParameteri because
ConvertToGLint always incorrectly converts a negative integer into
an unsigned integer in ValidateTexParameterBase.

BUG=angleproject:2371
TEST=angle_end2end_tests
     dEQP-GLES31.functional.debug.negative_coverage.get_error.texture.texparameter*
Change-Id: Id5baf3430ae574a083bcc40a7a8f7db1cb2d07ed
Reviewed-on: https://chromium-review.googlesource.com/933923Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>