staging: fbtft: cleanup error handling in fbtft_framebuffer_alloc()

staging: fbtft: cleanup error handling in fbtft_framebuffer_alloc()

The error handling in fbtft_framebuffer_alloc() mixes managed allocation
and plain allocation, and performs error handling in an order different
from the order in fbtft_framebuffer_release().

Fix them by moving vmem allocation closer to where it is used, and using
plain kzalloc() for txbuf allocation. Also remove the duplicate call to
fb_deferred_io_cleanup().

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Abdun Nihaal <abdun.nihaal@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20250701164537.243282-1-abdun.nihaal@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>