drm/nouveau/volt/gk20a: don't misuse kernel-doc comments

Change kernel-doc "/**" comments to common "/*" comments to prevent
kernel-doc warnings:

gk20a.c:49: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * cvb_mv = ((c2 * speedo / s_scale + c1) * speedo / s_scale + c0)
gk20a.c:49: warning: missing initial short description on line:
 * cvb_mv = ((c2 * speedo / s_scale + c1) * speedo / s_scale + c0)
gk20a.c:62: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * cvb_t_mv =
gk20a.c:62: warning: missing initial short description on line:
 * cvb_t_mv =
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@redhat.com>
Cc: nouveau@lists.freedesktop.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231231233633.6596-4-rdunlap@infradead.org

drivers/gpu/drm/nouveau/nvkm/subdev/volt/gk20a.c

@@ -45,7 +45,7 @@ static const struct cvb_coef gk20a_cvb_coef[] = {
 	/* 852 */ { 1608418, -21643, -269,     0,    763,  -48},
 };
 
-/**
+/*
  * cvb_mv = ((c2 * speedo / s_scale + c1) * speedo / s_scale + c0)
  */
 static inline int
@@ -58,7 +58,7 @@ gk20a_volt_get_cvb_voltage(int speedo, int s_scale, const struct cvb_coef *coef)
 	return mv;
 }
 
-/**
+/*
  * cvb_t_mv =
  * ((c2 * speedo / s_scale + c1) * speedo / s_scale + c0) +
  * ((c3 * speedo / s_scale + c4 + c5 * T / t_scale) * T / t_scale)