gpu: cdns-mhdp8546: fix call balance of mhdp->clk handling routines

If the clock mhdp->clk was not enabled in cdns_mhdp_probe(), it should not
be disabled in any path.

The return value of clk_prepare_enable() is not checked. If mhdp->clk was
not enabled, it may be disabled in the error path of cdns_mhdp_probe()
(e.g., if cdns_mhdp_load_firmware() fails) or in cdns_mhdp_remove() after
a successful cdns_mhdp_probe() call.

Use the devm_clk_get_enabled() helper function to ensure proper call
balance for mhdp->clk.

Found by Linux Verification Center (linuxtesting.org) with Klever.

Fixes: fb43aa0a ("drm: bridge: Add support for Cadence MHDP8546 DPI/DP bridge")
Signed-off-by: Vitalii Mordan <mordan@ispras.ru>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250214154632.1907425-1-mordan@ispras.ru