egl: check the correct function pointer

`.swap_interval` != `.SwapInterval`...

Fixes: 991ec1b81a76de24fd01 "egl: make platform's SwapInterval() optional"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102015
Cc: Cedric Sodhi <manday@openmail.cc>
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Tested-by: Cedric Sodhi <manday@openmail.cc>
2 files changed