drm/bridge: ti-sn65dsi86: fix a ternary type promotion bug

The ti_sn_aux_transfer() function returns ssize_t (signed long).  It's
supposed to return negative error codes or the number of bytes
transferred.  The "ret" variable is int and the "len" variable is
unsigned int.

The problem is that with a ternary like this, the negative int is first
type promoted to unsigned int to match "len" at this point it is a high
positive value.  Then when it is type promoted to ssize_t (s64) it
remains a high positive value instead of sign extending and becoming a
negative again.

Fix this by removing the ternary.

Fixes: b137406d ("drm/bridge: ti-sn65dsi86: If refclk, DP AUX can happen w/out pre-enable")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/YKOGogHasIyvF8nj@mwanda