Backport of "gst-libs: gl: Fix documentation typo and clarify gl_memory_texsubimage" into 1.18
Backport of !806 (merged) "gst-libs: gl: Fix documentation typo and clarify gl_memory_texsubimage".
Commits:
- 0ea3279d gst-libs: gl: Fix documentation typo and clarify gl_memory_texsubimage