Documentation: dmaengine: Correct reference to glReadPixels()

The author very likely meant "glReadPixels()" instead of
"glReadpielx()", which does not appear in the OpenGL API.

https://registry.khronos.org/OpenGL-Refpages/gl4/html/glReadPixels.xhtml



Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>
Link: https://lore.kernel.org/r/20241010-doc-dmaengine-glreadpixels-v1-1-8202e5834b13@amd.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>